1. Field of the Invention
The present invention relates to a method for fabricating a structure of etch-resistant metal/semiconductor compound on a substrate of semiconductor material using resistless electron beam lithography, more specifically a highly focused electron beam to produce a sub-micron structure of etch-resistant metal/semiconductor compound.
2. Brief Description of the Prior Art
The fabrication of ultra-small scale electronic devices requires efficient high resolution lithography techniques. Resist-based lithography processes are very frequently involved in these high resolution lithography techniques, and poly(methyl methacrylate) (PMMA) is the polymer most widely used as a resist for electron beam lithography applications (S. P. Beaumont, P. G. Bower, T. Tamamura, C. D. W. Wilkinson, Appl. Phys. Lett., 38, 438 (1991) and W. Chen, H. Ohmed, J. Vac. Sci. Technol., B 11, 2519 (1993)).
These types of lithographic processes suffer from several limitations which can become extremely constraining in the fabrication of sub-100 nm devices. These limitations include undesirable proximity effects in the resist and resolution limits imposed by the size of the polymer molecules. Proximity effects are produced when the exposed patterns are situated within the range of backscattered electrons. These electrons are primary electrons which collide with the substrate with a great angle to escape from the surface with a high energy in an area which may be considerably larger than the electron beam diameter. These high energy electrons expose the resist in an undesirable region. Current research efforts in lithography techniques include several resistless processes for defining patterns (see for example D. Wang, P. C. Hoyle, J. R. A. Cleaver, G. A. Porkolab, N. C. MacDonald, J. Vac. Sci. Technol., B 13, 1984 (1995) for electron beams; and H. Sugimura and N. Nakagiri, J. Vac. Sci. Technol, B 13, 1933 (1995) for a scanning probe technique).
The formation of a silicide layer is usually carried out by annealing samples of thin metal layers on silicon substrates in a conventional furnace with a controlled atmosphere of N.sub.2 -H.sub.2. This annealing technique requires several minutes to convert the metal film into silicide (see C. A. Chang, J. Appl. Phys., 58, 3258 (1985); C. A. Chang and A. Segmuller, J. Appl. Phys., 61, 201 (1987); C. A. Chang and W. K. Chu, Appl. Phys. Lett., 37, 3258 (1980); and C. A. Chang and J. M. Poate, Appl. Phys. Lett., 36, 417 (1980)).
New techniques involving Rapid Thermal Annealing (RTA) improve the process of the formation of silicide. RTA silicide films are significantly better than those formed by conventional annealing (C. A. Dimitriadis, Appl. Phys. Lett., 56, 143 (1990)), due to a shorter processing time (A. Torres, S. Kolodinski, R. A. Donaton, K. Roussel and H. Bender, SPIE, 2554, 185, (1995)).
More recently, several techniques of formation of silicide have been developed. These processes involve heating of metal-silicon interfaces using photons, electrons and ion beams (J. M. Poate and J. W. Mayer, Laser Annealing of Semiconductors, Academic Press, New York, 1982; J. Narayan, W. L. Brown and R. A. Lemons, Laser-Solids Interactions and Transient Processing of Materials, North-Holland, New York, 1983; and E. D'Anna, G. Leggieri and A. Luches, Thin Solids Films, 129, 93 (1985)). All these methods are based on the concept of forming silicide with localized heating near the surface. However, none of these techniques is intended as lithography processes, the heating occurring over the entire surface of the sample.